Substantial evidence suggests that the aging process impairs several aspects of kidney function. The goal of the present proposal is to determine the mechanism(s) whereby aging diminishes biochemical and functional response to several polypeptide hormones in well-defined renal epithelial cells. The effect of aging on growth, survival, ultrastructure and adenylate cyclase activity response to arginine vasopressin, parathyroid hormone and calcitonin will be examined in primary cell cultures of rabbit and human collecting tubule, proximal straight tubule and ascending limb of Henle. Techniques that will be utilized to assess the effect of aging in these cells include electron microscopy, assessment of DNA synthesis (3H-thymidine uptake) and Na-K ATPase activity (3H-ouabain binding), histocytochemistry and determination of the effect of pertussis and cholera toxins and forskolin on adenylate cyclase activity. Once primary cell cultures are characterized, cell lines of well-defined human and rabbit renal epithelia will be established and characterized. Parallel physiologic experiments will be undertaken using well-defined microdissected rabbit renal tubular epithelial cell segments studied in vitro. The effects of advancing age on renal tubular cell segment tranport, electrical potential difference, ultrastructure and cAMP response to selected hormones will be studied in renal tubules microdissected from all nephron segments. These studies will allow direct assessment of the effect of aging on the structure and function of several nephron epithelial cell segments. Together, the studies in the present proposal utilize physiologic, morphologic and biochemical techniques in an effort to clarify the effect of aging on renal tubular cell biology. These studies should also provide characterization of new cell model systems including characterization of human renal epithelial cells in culture.